Flexible polyurethane foams are resin parts having excellent rebound properties and are widely used as seat cushions or the like in vehicles such as automobiles.
Vehicle seat cushions are required to have excellent durability and small changes in cushion elasticity, hardness and thickness after along term of use. The vehicle seats also require appropriate hardness and elasticity to provide comfortable sitting (static comfort) and vibration absorbing properties to reduce vibrations from the road and to achieve comfortable ride (dynamic comfort). These properties of the vehicle seats are closely associated to the fatigue in long drive and significantly affect human safety.
On the other hand, from the viewpoint of the reduction of environmental load, there have been demands for plant-derived resins from plant resources as alternatives for the petroleum-derived resins from petroleum resources. Plants grow by photosynthesis absorbing CO2 in the atmosphere. The plant-derived resins obtained from such plant materials are therefore carbon neutral. In detail, the CO2 emissions by combustion of these resins are not added to the CO2 amount in the air. The plant-derived resins are therefore attractive materials that can contribute to the reduction of environmental load. Further, the prevention of the depletion of limited petroleum resources will increase its importance in the future, and active use of plant resources will be very effective means for that purpose.
Patent Literatures 1 and 2 propose flexible polyurethane foams used in vehicle seat cushions that are produced from plant resources such as starch, molasses, rice bran and castor oil.
However, existing polyurethane foams from plant resources generally do not have appropriate hardness, impact resilience and durability with good balance. In particular, producing foams having high impact resilience is difficult.
Patent Literature 3 then discloses a plant-derived polyurethane foaming composition comprising a combination of a plant-derived polyol and a low-monool polyol, and a polyurethane foam as a vehicle seat cushion material that has appropriate impact resilience, hardness and durability with good balance.
However, the impact resilience of the polyurethane foams according to Patent Literature 3 is as low as about 60%, and cushioning properties and touch are still unsatisfactory. Further improvements are necessary to meet market demands for vehicle seat comfort.